This invention relates to a differential current circuit breaker operating with a transductor circuit. The secondary winding of the transductor circuit is coupled in series between a measuring impedance and a generator, in particular a square wave generator, for alternating magnetization. An evaluation circuit is coupled to a tripping mechanism that acts via a breaker mechanism upon switching contacts in the conductors to be monitored. The evaluation circuit is coupled to a tap between the secondary winding and the measuring resistor. The resulting signal from the secondary winding is applied to the measuring resistor and is processed in the evaluation circuit to initiate the tripping process. This type of differential current circuit breaker is known and is described in European Patent No. A1-0 167 079.
Differential current circuit breakers are used to respond to leakage currents comprising filtered d.c. current, pulsating a.c. current (i.e. with aperiodic components), and a.c. current.
In the case of a square hysteresis loop, core material for the summation current transformer has relatively narrow, manufacturing tolerances as well as coercive field strength during saturation induction and remanent induction. In light of this, the tripping action for filtered d.c. current can be adjusted rather easily. However, for tripping alternating and pulsating currents, the induction range of the iron core is of considerable importance. As a rule, this induction range is not defined by the manufacturer, nor is it guaranteed in tolerances.
In practice, relatively large variances appear from core to core. In alternating and pulsating currents, the tripping values of a differential current circuit breaker can not be easily adjusted and require several processing steps. Thus, several compensating devices are usually provided for a differential current circuit breaker. There is a need for an improved differential current circuit breaker that can be easily and simply set to a desired response range within a sample series by using one frequency tuner.